The report of a positive blood culture Is a significant finding that is relayed to the doctor as soon as possible. in order to ensure that appropriate antibiotic coverage is selected, it is important to provide information as to the type of organism present. When the organism Is growing in a blood culture bottle, it must first be subcultured onto plates to obtain growth that can be used for identification and susceptibility testing. This frequently results in an overnight delay. Direct inoculation of Identification strips or other tests using growth from the bottle cannot be done reliably since there may be insufficient quantities of organism or the presence of blood may Interfere with accuracy of the result. We have found that the serum separator tube, normally used to prepare serum from blood, can be used to prepare a blood cell-free pellet of organism from positive blood culture bottles. The pellet contains a 6-8 fold concentration of organism, without red blood cell contamination, so that rapid tests can be performed to help determine the genus or species of organism on the same day that the broth culture is positive. These studies define the accuracy of tests using the serum- separator pellet.